Introduction of groundwater capillary rises using subgrid spatial variability of topography into the ISBA land surface model

Abstract

This paper presents a simple method for representing upward capillary fluxes from shallow groundwater into the unsaturated soil column of the large-scale hydrological models generally used at low resolution in global climate models. The groundwater scheme implemented in the Total Runoff Integrating Pathways river-routing model in a previous study is coupled with the Interaction between Soil Biosphere Atmosphere (ISBA) land surface model. In this coupling, the simulated water table depth acts as the lower boundary condition for the soil moisture diffusive equation. An original parameterization accounting for the subgrid topography inside each grid cell is proposed in order to compute this fully coupled soil lower boundary condition. The impact of this coupling on the simulated water budget is evaluated over France for the 1989-2009 period. Simulations are performed at high (1/12°) and low (0.5°) resolutions. Upward capillary fluxes induce a decrease in the simulated recharge from ISBA to the aquifers and contributes to an enhancement of the soil moisture memory. The simulated water table depths are then lowered, which induces a slight decrease in the simulated mean annual river discharges. These differences do not affect the comparison with observations. As a consequence, the simulated river discharges and water table heads compare still well with observations for the two soil bottom condition (free drain or fully coupled). It confirms the suitability of the coupling parameterization using subgrid spatial variability of topography. Compared to a free drain experiment, upward capillary fluxes at the bottom of the soil increase the mean annual evapotranspiration simulated over the aquifer domain by 3.12% and 1.54% at high and low resolutions, respectively. This increase can locally reach 50% and 30%, respectively.

Evaluation of Regional-Scale River Depth Simulations Using Various Routing Schemes within a Hydrometeorological Modeling Framework for the Preparation of the SWOT Mission

“…This relation is of the same order as the relation found by Arora and Boer (1999) and is very close to the relation established by Vergnes et al (2014), using data from all over France.…”

SURFEX v8.0 interface with OASIS3-MCT to couple atmosphere with hydrology, ocean, waves and sea-ice models, from coastal to global scales

“…the depth of the groundwater, and the grid-cell groundwater fraction (C WTD ). In other words, the WTD computed in CTRIP acts as the lower boundary condition for the ISBA soil moisture diffusive equation (Vergnes et al, 2014). For the floodplains, CTRIP sends to SURFEX the floodplain grid-cell fraction (C FP ) and the floodplain water mass flux to the land surface reservoir (W FP ).…”

Hydrological assessment of atmospheric forcing uncertainty in the Euro-Mediterranean area using a land surface model

“…To improve the simulation of river discharge and to assess the impacts of water abstractions, LSMs may progressively integrate groundwater modelling (see e.g. Vergnes et al, 2014) and lake and reservoir regulation (see e.g. Hanasaki et al, 2006;Pokhrel et al, 2012).…”

“…CC BY 4.0 License. Vergnes et al (2014) introduced the representation of capillary water rise from the groundwater reservoir, which provides the lower boundary condition for the moisture redistribution in the unsaturated soil column. To try to improve the modelled discharge response to rainfall events, the current Richards equations representation of water movement in unsaturated soil might be complemented with other parametrisations as, for instance, preferential flow in macro-pores (Beven and Germann, 2013).…”